The impaired control of muscle force in elderly adults can negatively impact quality of life. Various inputs to the motor neuron pool for a muscle could contribute to altered force control for healthy and frail elderly. The visuomotor contribution to force unsteadiness is not well characterized in healthy elderly and unknown in frail elderly. The limited information available is only for small hand muscles. The purposes are 1) to determine the contribution of visuomotor correction to force fluctuations in a hand muscle (FDI) and proximal leg muscle (KE) within the same individual young, health elderly, and frail elderly adults, 2) to quantify the role of central slowing and cutaneous sensory acuity in the impaired control, 3) to determine the functional significance of hand and leg muscle force fluctuations, and 4) to determine the visuomotor contribution to the variability of FDI and KE motor unit discharge. Young, healthy elderly and frail elderly adults will perform steady contractions under different visual feedback conditions to determine age-related differences in the processing of visuomotor information to maintain a steady muscle force. Reaction time and sensory acuity tests will determine the contribution of central slowing and sensory degradation. Hand dexterity and leg functional measures will provide a clinically relevant connection to function. The discharge of single motor units will be recorded in the FDI and KE muscles to provide information on a neural mechanism underlying the force fluctuations and changes with aging in two very different muscles. Although frail elderly adults exhibit neuromuscular and functional decline, mechanisms of force control in this group are not well understood. We hypothesize that frail elderly will exhibit a greater contribution of visuomotor processing, greater fluctuations in force, and greater motor unit variability, which will be explained in part by central slowing and sensory degradation. This project will determine some reasons that the elderly have more difficulty controlling their muscles. The control of different muscles will be measured in young, healthy elderly, and frail elderly adults to determine the role of impaired vision in the control of muscles. Greater knowledge of these changes in the nervous system of aging Americans can lead to the application of more effective intervention strategies to combat frailty and functional disability in the elderly. [unreadable] [unreadable]